In orthodontic treatment, whether or not to extract teeth has always been a controversial issue, and is also a more difficult issue for orthodontists. From the father of orthodontics Angle’s theory of non-extraction orthodontic treatment to date, has experienced nearly a century of constant change and repetition, Dr. Angle pursuit of ideal normal dentition, the requirement of retaining all the teeth in the mouth, and advocate the promotion of mastication to stimulate jawbone growth, to provide sufficient space for the teeth. However, it was later found that the growth of jawbone mainly depends on heredity, and the influence of acquired factors is limited. For malocclusion malocclusion with insufficient space, if the teeth are not extracted and corrected, its efficacy is unstable and prone to recurrence. His student, Dr. Tweed, based on a large number of clinical research results, proposed that the case of bimaxillary protrusion should be treated with extra-oral support and extraction of the first bicuspid, and achieved satisfactory results. As a result, extraction orthodontic treatment was popular for a while, sweeping the entire orthodontic community, and extraction orthodontic treatment became the mainstream of oral orthodontics. In the last decade or so, with the development of oral material science and the improvement of orthodontic technology, orthodontic force and orthopedic force are jointly applied to some cases with growth and development potentials, even if there is crowding of the teeth or irregularities between the upper and lower jaws, orthodontic treatment without extractions is often used to achieve success. Northwestern University orthodontics, for example, the extraction rate of 1940-1949 <10%; 1950-1959 45%; 1960-1969 >60%; 1970-1979 50%; 1980-1989 35%; 15% after 1990. Alexander believes that in the United States, about 25% of the cases must be extracted, about 25% of the cases do not have to be extracted orthodontic treatment. Alexander believes that in the United States about 25% of cases must be extracted, about 25% of cases do not need to be extracted, and 50% are borderline cases. In the orthodontic department of Peking University Stomatology Hospital, the number of extraction cases in 1996 was 64.60%. In the actual clinical work, whether to extract or not is sometimes still elusive, especially in borderline cases, and even the definition of borderline cases have different views on the criteria. Whether to extract or not is also related to the orthodontist’s own design tendency, orthodontic technical means and the patient’s own or parents’ imagination and degree of cooperation.